This invention relates generally to a rock bit for down-the-hole drilling and more particularly the rock drill bit having passages for the discharge of cuttings using a fluid operated percussive drill motor.
A continuing problem exists in providing an adequately controlled flow of a flushing medium to the multicutting bit inserts provided in the face of a rock drill bit. Removal of cuttings and debris from the face of a rock bit is vital, if such bit is to continue to drill efficiently and to have an economical service life. Cuttings removal is customarily done by the introduction of an exhaust fluid into or near the working bottom of the drilled hole, usually through the drill bit body itself. In established down-the-hole drilling practices, fluid turbulence and constricted flow circuits for the flushing fluid serve to erode the bit body rather variably, and thus reduces the overall effective working time.
Existing bits that are employed with downhole, pneumatically driven rock drills (DHD's), typically are provided with one or more machined passages leading into the bit face or are located on the periphery of the face. Such directly engage the rock bottom of the drilling bore hole. The fluid outlets act as dual means to exhaust the operating air from the DHD and for flushing rock cuttings and debris away from the working face, permitting their continuous removal from the bore hole.
Since all of the spent air that operates the DHD is exhausted across the bit face, usually from about the bit axis to the outer periphery of the bit, the high volumetric air flows used and the consequent fluid flow velocity across the bit face and about the adjacent skirt become substantial, causing strongly abrasive wear of the bit body. This is especially so near the periphery of the bit body.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.